Nitride Semiconductor Light Emitting Device and Fabrication Method Thereof

ABSTRACT

Provided is a nitride semiconductor light emitting device including: a first nitride semiconductor layer; an active layer formed above the first nitride semiconductor layer; and a delta doped second nitride semiconductor layer formed above the active layer. According to the present invention, the optical power of the nitride semiconductor light emitting device is enhanced, optical power down phenomenon is improved and reliability against ESD (electro static discharge) is enhanced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 14/201,883, filed Mar. 9, 2014; which is a continuation of U.S. application Ser. No. 13/585,451, filed Aug. 14, 2012, now U.S. Pat. No. 8,674,340, issued Mar. 18, 2014; which is a continuation of U.S. application Ser. No. 12/849,265, filed Aug. 3, 2010, now U.S. Pat. No. 8,278,646, issued Oct. 2, 2012; which is a continuation of U.S. application Ser. No. 11/719,929, filed May 22, 2007, now U.S. Pat. No. 7,791,062, issued Sep. 7, 2010; which is the U.S. national stage application of International Patent Application No. PCT/KR2005/004120, filed Dec. 5, 2005; which claims priority to Korean Patent Application No. 10-2004-0111087, filed Dec. 23, 2004, all of which are incorporated herein by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention is relative to a nitride semiconductor light emitting device and fabrication method thereof, and to a nitride semiconductor light emitting device and a fabrication method thereof that can increase the optical power and enhance the reliability by increasing a hole carrier concentration contributing to the electric conductivity in an electrode contact layer to increase the recombination probability of electrons and holes.

2. Background Art

A schematic stack structure of a general nitride semiconductor light emitting device and a fabrication method thereof will now be described.

FIG. 1 is a sectional view of a general nitride semiconductor light emitting device.

Referring to FIG. 1, a conventional nitride semiconductor light emitting device includes a substrate 101, a buffer layer 103, an n-GaN layer 105, an active layer 107 and a p-GaN layer 109. Herein, the substrate 101 can be exemplified by a sapphire substrate.

A fabrication method of the nitride semiconductor light emitting device will now be described. In order to minimize the occurrence of crystal defects due to differences in the lattice constants and the thermal expansion coefficients of the substrate 101 and the n-GaN layer 105, a GaN-based nitride or an AlN-based nitride having an amorphous phase at a low temperature is formed as the buffer layer 103.

The n-GaN layer 105 doped with silicon at a doping concentration of 10¹⁸/cm³ is formed at a high temperature as a first electrode contact layer. Thereafter, the growth temperature is lowered and the active layer 107 is formed. Thereafter, the growth temperature is again elevated and the p-GaN layer 109 doped with magnesium (Mg) and having a thickness range of 0.1-0.5 μm is formed as a second electrode contact layer. The nitride semiconductor light emitting device having the aforementioned stack structure is formed in a p-/n-junction structure which uses the n-GaN layer 105 as the first electrode contact layer and uses the p-GaN layer 109 as the second electrode contact layer.

Also, a second electrode material formed on the second electrode contact layer is limited depending on a doping type of the second electrode contact layer. For example, in order to decrease the contact resistance between the second contact material and the p-GaN layer 109 having a high resistance component and enhance the current spreading, a thin transmissive resistance material of a Ni/Au alloy is used as the second electrode material.

To form the p-GaN layer 109 used as the second electrode contact layer, the p-/n-junction light emitting device using the nitride semiconductor employs a doping source of Cp₂Mg or DMZn. In the case of DMZn, since Zn is in ‘deep energy level’ within the p-GaN layer 109 and has a very high activation energy, the hole carrier concentration serving as a carrier when a bias is applied is limited to about 1×10¹⁷/cm³. Accordingly, Cp₂Mg MO (metal organic) having a low activation energy is used as the doping source.

Also, when the Mg-doped p-GaN layer 109 having a thickness range of 0.1-0.5 μm is grown using a doping source of Cp₂Mg at the same flow rate or by sequentially varying the flow rate of Cp₂Mg, hydrogen (H) gas separated from the doping source and NH₃ carrier gas are combined to form an Mg—H complex, in the p-GaN layer 109, which shows a high resistance insulation characteristic of more than ˜10⁶ Ω. Accordingly, in order to emit light during the recombination process of holes and electrons in the active layer 107, an activation process is essentially required to break the bond of Mg—H complex. Since the Mg-doped p-GaN layer 109 has a high resistance, it cannot be used without any change. The activation process is performed through an annealing process at a temperature range of 600° C.-800° C. in an ambient of N₂, N₂/O₂. However, since Mg existing in the p-GaN layer 109 has a low activation efficiency, it has a relatively high resistance value compared with the n-GaN layer 105 used as the first electrode contact layer. In real circumstance, after the activation process, the atomic concentration of Mg in the p-GaN layer 109 is in a range of 10¹⁹/cm³-10²⁰/cm³, and the hole carrier concentration contributing to a pure carrier conductivity is in a range of 10¹⁷/cm³-10¹⁸/cm³, which correspond to a difference of maximum 10³ times. It is also reported that the hole mobility is 10 cm²/vsec, which is a very low value. FIG. 2 is a schematic view showing a sectional structure of the conventional Mg-doped p-GaN layer and an Mg profile inside the Mg-doped p-GaN layer after the activation process is performed. Referring to FIG. 2, it can be seen that the Mg atomic concentration and the hole carrier concentration show a difference of maximum 10³ times.

Meanwhile, the Mg atomic concentration remaining in the p-GaN layer 109 without a complete activation causes many problems. For example, light emitting from the active layer toward the surface is trapped to lower the optical power, or when a high current is applied, heat is generated due to a relatively high resistance value, so that the life time of the light emitting device is shortened to have a fatal influence on the reliability. Especially, in the case of a large size/high power 1 mm×1 mm light emitting device using a flip chip technique, since a current of 350 mA which is very higher than a conventional current of 20 mA is applied, a junction temperature of more than 100° C. is generated at a junction face, having a fatal influence on the device reliability and causing a limitation to product application in future. The generated much heat is caused by an increase of resistance component due to the Mg atomic concentration remaining in the p-GaN layer 109 used as the second electrode contact layer without being activated as a carrier, and a rough surface property due to the increase of the resistance component.

Also, in the general p-/n-junction light emitting device, the n-GaN layer 105 used as the first electrode contact layer can easily control the hole concentration within 5-6×10¹⁸/cm³ within a critical thickness ensuring the crystallinity in proportional to the silicon doping concentration depending on an increase in the flow rate of SiH₄ or Si₂H₆, whilst in the p-GaN layer 109 used as the second electrode contact layer, the hole concentration substantially serving as carriers is limited within a range of 1-9×10¹⁷/cm³ although the flow rate of Cp₂Mg is increased and Mg atoms of more than maximum ˜10²⁰/cm³ are doped. To this end, the conventional light emitting device is made in a p-/n-junction structure having an asymmetric doping profile.

As aforementioned, the low carrier concentration and high resistance component of the p-GaN layer 109 used as the second electrode contact layer cause the light emitting efficiency to be decreased.

To solve the above problem, a conventional method for increasing the optical power by employing Ni/Au TM (transparent thin metal) having a good transmission and a low contact resistance has been proposed. However, the conventional method badly influences the device reliability when being applied to a large size/high power light emitting device. This problem still remains unsettled in the light emitting devices using the GaN semiconductor.

BRIEF SUMMARY Technical Problem

The present invention provides a nitride semiconductor light emitting device and fabrication method thereof that can enhance the property of p-GaN layer constituting the nitride semiconductor light emitting device.

Also, the present invention provides a nitride semiconductor light emitting device and fabrication method thereof that can enhance the optical power and reliability.

In addition, the present invention provides a nitride semiconductor light emitting device and fabrication method thereof that can overcome the problems caused by the low hole carrier concentration and mobility of the Mg-doped p-GaN layer used as the second electrode contact layer and a high resistance component of Mg atomic concentration (including Mg—H complex) remaining completely inactivated in the p-GaN layer, and enhance the optical power and reliability.

Technical Solution

There is provided a nitride semiconductor light emitting device including: a first nitride semiconductor layer; an active layer formed above the first nitride semiconductor layer; and a delta doped second nitride semiconductor layer formed above the active layer.

In another aspect of the present invention, there is provided a nitride semiconductor light emitting device including: a buffer layer; a first nitride semiconductor layer formed above the buffer layer; a first electrode contact layer formed above the first nitride semiconductor layer; an active layer formed above the first nitride semiconductor layer in a single quantum well structure or a multi quantum well structure comprised of a well layer and a barrier layer; and a delta doped second nitride semiconductor layer formed above the active layer.

In another aspect of the present invention, there is provided a method of fabricating a nitride semiconductor light emitting device, the method including: forming a buffer layer above a substrate; forming a first nitride semiconductor layer above the buffer layer; forming an active layer above the first nitride semiconductor layer; and forming a delta doped second nitride semiconductor layer above the active layer.

Advantageous Effects

According to the present invention, the characteristic of the p-GaN layer constituting the nitride semiconductor light emitting device is enhanced, the optical power of the nitride semiconductor light emitting device is enhanced, the optical power down phenomenon is improved, and the reliability against ESD (Electro Static Discharge) is enhanced.

DESCRIPTION OF DRAWINGS

The spirit of the present invention will be understood more apparently from the accompanying drawings. In the drawings:

FIG. 1 is a schematic view showing a stack structure of a general nitride semiconductor light emitting device;

FIG. 2 is a schematic view showing a sectional structure of the conventional Mg-doped p-GaN layer and an Mg profile inside the Mg-doped p-GaN layer after the activation process is performed;

FIG. 3 is a schematic view illustrating a Cp₂Mg delta doping flow rate according to a growth time;

FIG. 4 is a graph showing an Mg doping profile before and after a subsequent activation process after a crystal growth for a Cp₂Mg delta doped p-GaN is completed;

FIG. 5 is a graph showing an electric field profile after a subsequent activation process of a Cp₂Mg delta doped p-GaN layer is completed;

FIG. 6 is a schematic view showing a stack structure of a nitride semiconductor light emitting device according to a first embodiment of the present invention; and

FIG. 7 is a schematic view showing a stack structure of a nitride semiconductor light emitting device according to a second embodiment of the present invention.

DETAILED DESCRIPTION Best Mode

Hereinafter, an embodiment according to the spirit of the present invention will be described with reference to the accompanying drawings.

The present invention is characterized in that in the fabrication method of a nitride semiconductor, a Cp₂Mg delta doping process is performed to grow a p-GaN layer, and the Cp₂Mg delta doping process will be described with reference to FIGS. 3 to 5.

FIG. 3 is a schematic view illustrating a Cp₂Mg delta doping flow rate according to a growth time.

Referring to FIG. 3, after an active layer emitting light is grown, an undoped GaN layer of less than 200 Å is grown so as to protect a “V” pit defect formed during the growth of the active layer, and the flow rate of Cp₂Mg is adjusted from 0 cc to 1000 cc within a thickness range of 10-200 Å to form a delta doped GaN layer. FIG. 3 shows an Mg-delta doped GaN grown by consecutively repeating one period consisting of undoped GaN layer/delta doped GaN layer. In the above crystal growth method, only the flow rate of Cp₂Mg is changed, the growth temperature is fixed to 1000° C. and the other conditions are fixed so as to maintain the crystallinity.

In growing the Mg-delta doped GaN layer, the thickness of each of the undoped GaN layer and the delta doped GaN layer constituting one period may be varied. Also, in repeatedly growing one period of undoped GaN layer/delta doped GaN layer, the dose at each period may be varied. At this time, an overall thickness of the two layers forming one period can be adjusted within a thickness range of 10-300 Å.

FIG. 4 is a graph showing an Mg doping profile before and after a subsequent activation process after a crystal growth for a Cp₂Mg delta doped p-GaN is completed.

Referring to FIG. 4, when Cp₂Mg delta doping of the same amount is repeated at a constant period before the subsequent activation process, the delta doped GaN layer having a sharp Mg doping profile can be obtained at a boundary between the undoped GaN layers. Thereafter, while the subsequent activation process is performed, Mg is diffused into the undoped GaN layers of both sides, so that a wide Mg doping profile is obtained. Through the above subsequent activation process, the p-GaN layer has a uniform Mg doping profile in whole.

In general, when a forward bias is applied to the undoped GaN layer, it can be seen that the operating voltage increases. In the present invention, the operating voltage can be effectively lowered to less than 3.5 V (20 mA) to increase the optical power of the light emitting device by controlling the thickness of the Cp₂Mg delta doped p-GaN layer and the thickness of the undoped GaN layer.

FIG. 5 is a graph showing an electric field profile after a subsequent activation process of a Cp₂Mg delta doped p-GaN layer is completed.

Referring to FIG. 5, it can be seen that the hole carrier concentration profile is relatively high in the Cp₂Mg delta doped regions periodically repeated. Therefore, in the Cp₂Mg delta doped regions, potential increases to form an electric field doping. Accordingly, like in an HEMT structure 2 DEG (two dimensional electronic well layer) that is a high speed switching device using an energy bandgap difference (AlGaN/GaN junction), potential well can be formed to uniformly and effectively control the flow of holes likewise to effectively control a two-dimensional flow of electrons. In conclusion, it can be seen that hole injection efficiency is increased by the potential well.

As can be seen from the above description, the p-GaN layer grown by the conventional art has a problem that when a forward bias is applied, a high resistance component thereof sharply decreases current flow in inverse proportion with a distance from an electrode contact surface to an upper surface thereof, whilst in the present invention, the potential well layer can more effectively increase the current density to enhance the optical power of the light emitting device.

Also, by the Cp₂Mg delta doping, since the doping element is uniformly, repeatedly and periodically doped at a relatively very small amount and then the activation process for the p-GaN layer is optimized and performed, the atomic concentration of Mg, Mg—H complex and the like existing therein can be decreased to suppress the resistance component as much as possible. In other words, the present invention increases the hole carrier concentration purely contributing to the electric conductivity to thereby increase the recombination probability with electrons and in the long run effectively increase the optical power. Thus, the present invention provides a high level crystal growth technique that can decrease the resistance component to enhance the reliability of the light emitting device.

Hereinafter, a concrete embodiment of the nitride semiconductor light emitting device according to the present invention will be described.

FIG. 6 is a schematic view showing a stack structure of a nitride semiconductor light emitting device according to a first embodiment of the present invention. Referring to FIG. 6, the nitride semiconductor light emitting device according to the present embodiment includes a substrate 401, a buffer layer 403, an In-doped GaN layer 405, an n-GaN layer 407, a low-mole In-doped GaN layer or low-mole InGaN layer 409, an active layer 411, and an Mg-delta doped p-GaN layer 413. The Mg-delta doped p-GaN layer 413 has been described in detail with reference to FIGS. 3 to 5.

Hereinafter, a fabrication method of the nitride semiconductor light emitting device according to a first embodiment will be described in more detail.

First, in the present embodiment, only H₂ carrier gas is supplied onto the sapphire substrate 401 at a high temperature to clean the sapphire substrate 401. Thereafter, in step of decreasing the growth temperature to 540° C., NH₃ source gas is supplied to perform a nitridation of the sapphire substrate 401, for example for 7 minutes.

Thereafter, the buffer layer 403 having a 1^(st) AlInN/1^(st) GaN/2^(nd) AlInN/2^(nd) GaN structure is grown to a thickness of about 500 Å. Herein, the buffer layer 403 can be formed in a structure selected from the group consisting of a stack structure of AlInN/GaN, a super lattice structure of InGaN/GaN, a stack structure of In_(x)Ga_(1−x)N/GaN, and a stack structure of Al_(x)In_(y)Ga_(1−(x+y))N/In_(x)Ga_(1−x)N/GaN. Then, the growth temperature is increased up to 1060° C. for 6 minutes, the low temperature buffer layer 403 is recrystallized in a mixture ambient of NH₃ source gas and H₂ carrier gas for 2 minutes, and at the same growth temperature, the indium-doped GaN layer 405 having about 2 μm thickness is grown in a single crystal.

Thereafter, the growth temperature is decreased to 1050° C., and the n-GaN layer 407 co-doped with silicon and indium at the same growth temperature is grown to a thickness of 2 μm. The n-GaN layer 407 is used as the first electrode layer.

Also, to adjust the strain of the active layer 411, the low-mole In-doped GaN layer or low-mole InGaN layer 409 having 5% indium content (wavelength: 480 nm) is grown to a thickness of 300 Å at 750° C. The indium content can be adjusted in a range of 1-5%. The low-mole In-doped GaN layer or low-mole InGaN layer 409 is intentionally controlled in ‘spiral growth mode’ having a uniform profile. Herein, in the low-mole In-doped GaN layer or low-mole InGaN layer 409, as the ‘spiral density’ intentionally controlled increases, the area of the active layer 411 increases. Accordingly, the low-mole In-doped GaN layer or low-mole InGaN layer 409 can perform a role that can increase the light emitting efficiency.

Thereafter, at the same growth temperature, the active layer 411 having a single quantum well (SQW) of undoped InGaN/InGaN structure is grown. In the grown active layer 411, the barrier layer has an indium content of less than 5% and a thickness of about 250 Å. At this time, the active layer 411 can be formed in the multi quantum well layer.

Thereafter, the growth temperature is again increased to 1000° C., an overall thickness is fixed to 0.1 μm, the flow rate of TMGa is also fixed, and only the flow rate of Cp₂Mg is switched on/off from 0 cc to 1000 cc to thereby perform the delta doping process. In order to effectively perform the Cp₂Mg delta doping, after the active layer 411 emitting light is grown, the undoped GaN layer is first grown in a thickness range of 10-200 Å to completely protect the active layer 411 such that Mg atoms are not internally diffused into the “V” pit crystal formed on a surface of the active layer 411, and then the Cp₂Mg delta doping process is performed in a thickness range of 10-200 Å. The Cp₂Mg delta doping process sets the undoped GaN/delta doped GaN structure as one period and continuously repeats the one period within an overall thickness of 0.1 μm to form a light emitting device having a p-/n-junction structure such that resistance component is decreased by Mg atomic concentration (including Mg atomic and Mg—H complex) after the activation and uniform carrier concentration is obtained.

After the nitride semiconductor light emitting device is completed by the aforementioned processes, mesa etching is performed using an ICP etching apparatus and the nitride semiconductor light emitting device is made in a size of 330 μm×205 μm. Electrical property variation of the fabricated nitride semiconductor light emitting device is analyzed and investigated to verify its performance. As a result, the operating voltage (20 mA) in a forward bias is below 3.4 V, which is the same value as that of the conventional art, but the optical power is increased by 50-100%.

Why the optical power is increased is that an inner diffusion into the “V” pit defect formed in the surface of the active layer emitting light is suppressed, and an absolute amount of Mg atomic (including Mg—H complex) remaining in the layer after the subsequent activation process is decreased by an Mg doping profile lower than that of the conventional art, but the hole carrier concentration contributing to the electric conductivity is increased.

FIG. 7 shows a nitride semiconductor light emitting device according to a second embodiment of the present invention.

Referring to FIG. 7, the nitride semiconductor light emitting device according to a second embodiment of the present invention includes a substrate 401, a buffer layer 403, an In-doped GaN layer 405, an n-GaN layer 407, a low-mole In-doped GaN layer or low-mole InGaN layer 409, an active layer 411, an Mg-delta doped p-GaN layer 413, and an n-InGaN layer 515.

Compared with the first embodiment, the above second embodiment has a difference in that the nitride semiconductor light emitting device further includes the n-InGaN layer 515. Therefore, only the n-InGaN layer 515 will be additively described and descriptions of other elements will be referred from that of the first embodiment.

To fabricate an n-/p-/n-junction structure light emitting device, in addition to the p-/n-junction structure light emitting device, the second embodiment of the present invention grows the Mg-delta doped p-GaN layer 413 and then grows the n-InGaN layer 515 to use as the second electrode contact layer.

The n-InGaN layer 515 used as the second electrode contact layer is grown to a thickness of 50 Å with being doped with silicon at a growth temperature decreased to 800° C. in a mixture gas ambient of NH₃ source gas and N₂ carrier gas. At this time, the n-InGaN layer 515 is used as the second electrode contact layer and is designed to have the super grading (SG) structure in which indium content is adjusted to control the energy bandgap profile on whole. By the aforementioned method, the n-/p-/n-junction structure nitride semiconductor light emitting device can be obtained.

MODE FOR INVENTION

In addition to the above embodiments, a plurality of other examples can be provided on the basis of the same spirit.

First, a transparent electrode may be further formed on the n-InGaN layer 515. The transparent electrode can be formed of one selected from the group consisting of ITO, IZO(In—ZnO), GZO(Ga—ZnO), AZO(Al—ZnO), AGZO(Al—Ga ZnO), IGZO(In—Ga ZnO), IrO_(x), RuO_(x), RuO_(x)/ITO, Ni/IrO_(x)/Au, and Ni/IrO_(x)/Au/ITO.

Also, while the second embodiment illustrates that the n-InGaN layer 515 is formed as the second electrode contact layer, an n-InGaN/InGaN super latttice structure may be formed as the second electrode contact layer. Alternatively, a Si-doped GaN layer may be further formed between the n-InGaN/InGaN super lattice layer and the Mg-delta doped p-GaN layer 413.

In addition, the first and second embodiments illustrate that Mg is delta doped in the delta doping process. However, through a similar process, Mg—Al, Mg—Al—In or the like as well as Mg can be delta doped. At this time, TMAl, TMIn MO (metal organic) can be used as a doping source.

Further, the delta doped p-GaN layer can be formed with one period consisting of undoped AlGaN/delta doped p-GaN structure, the two layers constituting the one period can be repeatedly grown at least two times, the undoped AlGaN layer is grown within a thickness range of 10-300 Å with an Al composition range of 0.01-0.02.

Furthermore, the delta doped p-GaN layer can be formed with one period consisting of undoped InGaN/delta doped p-GaN structure, the two layers constituting the one period can be repeatedly grown at least two times, the undoped InGaN layer is grown within a thickness range of 10-300 Å with an Al composition range of 0.01-0.1.

Also, the delta doped p-GaN layer can be formed with one period consisting of undoped GaN/undoped AlGaN cap/delta doped p-GaN structure, the three layers constituting the one period can be repeatedly grown at least two times, the undoped AlGaN cap layer is grown within a thickness range of 5-200 Å with an Al composition range of 0.01-0.02.

Additionally, the delta doped p-GaN layer can be formed with one period consisting of undoped InGaN/undoped AlGaN cap/delta doped p-GaN structure, the three layers constituting the one period can be repeatedly grown at least two times, the undoped AlGaN cap layer is grown within a thickness range of 5-200 Å with an Al composition range of 0.01-0.02.

Also, in the first and second embodiments, the n-GaN layer serving as the first electrode contact layer can be an n-GaN layer formed by a co-doping of Si and In, and it can be formed at a doping concentration of 1-9×10¹⁹/cm³ in a thickness range of 1-4 μm.

Additionally, the first electrode contact layer can be formed with one period consisting of undoped-AlGaN/doped-GaN super lattice structure, the two layers constituting the one period can be repeatedly grown at least two times with an overall thickness of 1-2 μm and an Al composition of 0.05-0.3. The doped-GaN layer can be formed within a thickness range of 200-500 Å.

Further, the active layer can be made in a single quantum well structure or a multi quantum well structure comprised of well layer/SiNx cluster layer/barrier layer, and the SiNx cluster layer can be grown by a Si-delta doping method. The SiNx cluster layer can be grown by the Si-delta doping using a doping source of SiH₄ or SiH₆ alone.

INDUSTRIAL APPLICABILITY

According to the nitride semiconductor light emitting device and fabrication method thereof provided by the present invention, the optical power is enhanced, the power down phenomenon is improved, and the reliability against ESD (Electro Static Discharge) is enhanced.

Also, the present invention can be applied to a lighting apparatus requiring high optical power and high reliability. 

What is claimed is:
 1. A light emitting device comprising: a first conductive type semiconductor layer; an active layer on the first conductive type semiconductor layer; and a second conductive type semiconductor layer on the active layer; wherein the second conductive type semiconductor layer comprises a delta doped p-type semiconductor layer on the active layer.
 2. The light emitting device according to claim 1, wherein the delta doped p-type semiconductor layer includes at least a first p-type nitride semiconductor layer near the active layer and at least a delta doped second p-type nitride semiconductor layer that goes away from the active layer.
 3. The light emitting device according to claim 2, wherein a dopant concentration of the delta-doped second p type nitride semiconductor layer is higher than a dopant concentration of the first p-type nitride semiconductor layer.
 4. The light emitting device according to claim 2, wherein the dopant concentration of the delta-doped second p-type nitride semiconductor layer is non-linearly decreased toward the first p-type nitride semiconductor layer.
 5. The light emitting device according to claim 2, wherein the delta-doped second p-type nitride semiconductor layer has a maximum dopant concentration and the first p-type nitride semiconductor layer has a minimum dopant concentration.
 6. The light emitting device according to claim 2, wherein the first conductive type nitride semiconductor layer comprises a GaN layer and the delta doped second p-type nitride semiconductor layer comprises a GaN layer.
 7. The light emitting device according to claim 2, wherein the first conductive type nitride semiconductor layer comprises a AlGaN layer and the delta doped second p-type nitride semiconductor layer comprises a GaN layer.
 8. The light emitting device according to claim 2, wherein the first conductive type nitride semiconductor layer comprises a InGaN layer and the delta doped second p-type nitride semiconductor layer comprises a GaN layer.
 9. The light emitting device according to claim 1, wherein the second conductive type semiconductor layer includes a p-type dopant, wherein the second conductive type semiconductor layer has a doping profile comprising a plurality of peaks.
 10. The light emitting device according to claim 9, wherein the second conductive type semiconductor layer comprises a p-type GaN layer and a p-type AlGaN layer, and wherein the plurality of peaks are disposed in the p-type GaN layer.
 11. A light emitting device comprising: a first nitride semiconductor layer; an active layer on the first nitride semiconductor layer; a second nitride semiconductor layer on the active layer; and wherein the active layer includes a quantum well structure for emitting light, wherein the first nitride semiconductor layer includes a super lattice structure having at least two layers, and wherein the second nitride semiconductor layer includes a p-type impurity, the p-type impurity having a doping profile.
 12. The light emitting device according to claim 11, wherein the doping profile comprises a first doping portion that has a minimum doping concentration and a second doping portion that has a maximum doping concentration.
 13. The light emitting device according to claim 11, wherein the first doping portion is near the active layer and the second doping portion goes away from the active layer.
 14. The light emitting device according to claim 11, wherein the doping profile has a curve that non-linearly decreases from the maximum doping concentration to the minimum doping concentration.
 15. The light emitting device according to claim 11, wherein the first doping portion and the second doping portion have the same dopants.
 16. The light emitting device according to claim 11, wherein the doping profile has a wide doping profile obtained by that dopants are diffused from the second doping potion to the first doping portion.
 17. The light emitting device according to claim 11, wherein the second nitride semiconductor layer comprises a p-type AlGaN layer and the p-type AlGaN layer includes Mg—Al—In.
 18. The light emitting device according to claim 11, wherein the first conductive type semiconductor layer comprises an n-GaN layer formed by a Si—In simultaneous doping.
 19. The light emitting device according to claim 11, wherein the second conductive type semiconductor layer comprises a p-type AlGaN layer and a p-type GaN layer and wherein p-type dopant of at least one portion of the p-type GaN layer is more heavily doped than p-type dopant of the p-type AlGaN layer.
 20. The light emitting device according to claim 11, wherein the first conductive type semiconductor layer comprises at least two times AlGaN/GaN super lattice structure of at least two layers. 